We have previously used ESI-MS to probe changes in the conformational states of proteins in well-equilibrated solutions. The basis for this probe was the observation that the charge states of electrosprayed proteins in the gas phase depend on the conformational states of the protein in solution. We now extend our earlier studies to investigate rapid (millisec) changes in the conformational states of proteins in heated electrospray droplets. This study demonstrates that special conditions are required to induce conformational changes in proteins on the millisecond time scale. Conversely, because conformational changes in proteins often occur on time-scales that are slow compared with the life-time of electrospray droplets, it proves feasible to deduce information concerning conformational changes of proteins in the electrospray solution prior to spraying A manuscript describing our results was published (Mirza and Chait, Int. J. Mass Spectrometry and Ion Processes 162, (1997) 173-181).